Defines a generalized type-specific comparison method that a value type or class implements to order or sort its instances.
mscorlib (in mscorlib.dll)
Public Interface IComparable
Compares the current instance with another object of the same type and returns an integer that indicates whether the current instance precedes, follows, or occurs in the same position in the sort order as the other object.
This interface is implemented by types whose values can be ordered or sorted. It requires that implementing types define a single method, CompareTo(Object), that indicates whether the position of the current instance in the sort order is before, after, or the same as a second object of the same type. The instance's IComparable implementation is called automatically by methods such as Array.Sort and ArrayList.Sort.
The implementation of the CompareTo(Object) method must return an Int32 that has one of three values, as shown in the following table.
Less than zero
The current instance precedes the object specified by the CompareTo method in the sort order.
This current instance occurs in the same position in the sort order as the object specified by the CompareTo method.
Greater than zero
This current instance follows the object specified by the CompareTo method in the sort order.
All numeric types (such as Int32 and Double) implement IComparable, as do String, Char, and DateTime. Custom types should also provide their own implementation of IComparable to enable object instances to be ordered or sorted.
The following example illustrates the implementation of IComparable and the requisite CompareTo method.
Public Class Temperature
' The temperature value
Protected temperatureF As Double
Public Overloads Function CompareTo(ByVal obj As Object) As Integer _
If obj Is Nothing Then Return 1
Dim otherTemperature As Temperature = TryCast(obj, Temperature)
If otherTemperature IsNot Nothing Then
Throw New ArgumentException("Object is not a Temperature")
Public Property Fahrenheit() As Double
Set(ByVal Value As Double)
Me.temperatureF = Value
Public Property Celsius() As Double
Return (temperatureF - 32) * (5/9)
Set(ByVal Value As Double)
Me.temperatureF = (Value * 9/5) + 32
Public Module CompareTemperatures
Public Sub Main()
Dim temperatures As New ArrayList
' Initialize random number generator.
Dim rnd As New Random()
' Generate 10 temperatures between 0 and 100 randomly.
For ctr As Integer = 1 To 10
Dim degrees As Integer = rnd.Next(0, 100)
Dim temp As New Temperature
temp.Fahrenheit = degrees
' Sort ArrayList.
For Each temp As Temperature In temperatures
' The example displays the following output to the console (individual
' values may vary because they are randomly generated):
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Available since 8.NET Framework
Available since 1.1Portable Class Library
Supported in: portable .NET platformsSilverlight
Available since 2.0Windows Phone Silverlight
Available since 7.0Windows Phone
Available since 8.1